The present invention is related to a device for layerwise manufacturing of a three-dimensional object.
Such devices are known in the prior art for example as devices for stereolithography, laser sintering etc.
Thus, for example a device for layerwise manufacturing of an object by laser sintering is known to the applicant, which has a support for positioning of the object relative to a work surface and a device for applying a powder that can be solidified by electromagnetic radiation. The apparatus comprises a laser. The laser beam that has been generated by the laser is focussed via lenses onto a spot within the work surface by a focussing device and solidifies the powder. In particular, when using plastics as powder material, volatile decomposition and reaction products escape from the powder in the process, which deposit on the lens and thus more and more reduce the transparency of the lens in the course of the manufacturing process. This leads to the situation that the laser beam is less and less transmitted, whereby its intensity in the work surface decreases. Due to the decreasing intensity the quality of the object to be manufactured degrades. In order to avoid this situation, a safety glass is placed in front of the lens, the safety glass being blown with nitrogen from several nozzles. However, as the nitrogen only partially overflows over the safety glass and as no flow is present between the nozzles, at these positions the contaminations deposit. Therefore, the safety glass has to be removed and cleaned after each building process.
In order to solve this problem EP 0 785 838 proposes a device, wherein the focussing device comprises an annular nozzle adjacent to the surface of the lens that is facing the work surface, which with its output side is directed towards the surface of the lens in such a way that an escaping flow tangentially runs along the surface of the lens towards the centre and which at the input side is connected to a source of a gas under pressure as e.g. nitrogen in such a way, that it can be disconnected.